This invention relates generally to a dispenser of the pressure accumulating type, and is an improvement over my earlier U.S. Pat. No. 4,050,613. More particularly, the present pump includes a modified plunger/accumulator designed to avoid unwanted dribbles or drips after the discharge passage is thereby closed.
Dispensers and sprayers of the pressure accumulating type, disclosed in the aforementioned patent application and patent, have a plunger member which reciprocates on a hollow stationary piston in response to the force of return spring from below and hydraulic force from above. The plunger functions as a discharge valve which closes in response to spring pressure as it returns to its seated position against the underside of the plunger head, the discharge passage being formed in the plunger head and extending to the atmosphere from an accumulation chamber defined by a downwardly directed blind socket formed at the underside of the plunger head for snugly slidably receiving the plunger. Thus, upon depression of the plunger head, pressure within the primed pump chamber increases within the accumulation chamber to a degree sufficient to overcome the opposing force of the spring whereupon the plunger moves relative to the plunger head to thereby open the discharge. Dispensing of product will continue under pressure through the open discharge passage so long as the hydraulic pressure in the accumulation chamber continues to overcome the opposing force of the return spring. When the spring force takes over, i.e., upon insufficient finger pressure exerted on the plunger head or upon discharge of the pump chamber and accumulation chamber contents near the end of the plunger downstroke, the plunger automatically reseats within the plunger head socket to thereby close the discharge passage. As the pump chamber expands during the ensuing plunger upstroke, a new charge of product is drawn into the pump chamber through the valve controlled inlet contained within the hollow stationary piston.
Although the aforedescribed dispensing pump operates quite efficiently and effectively in discharging product after the discharge is closed, an optional approach is available for avoiding any unexpected discharge at the commencement of the recharge stroke of the plunger.
If the plunger head of the example the pump according to the aforementioned application or my earlier patent U.S. Pat. No. 4,050,613, is subjected to lateral or eccentric forces during the dispensing operation, as when the operator reciprocates the head non-axially, such forces tend to induce a frictional load between the plunger and discharge valve elements which can permit the plunger-discharge valve to be momentarily held open at the end of the plunger downstroke with a small quantity of product remaining within the discharge passage. When the actuating force on the head is relieved, even slightly, the frictional holding force or brake on the plunger is relaxed. This then causes the return spring to shift the plunger immediately to its discharge valve closing position. Thus, the small amount of product which had been left in the discharge passage at the end of the discharge stroke is now suddenly purged at the start of the plunger intake stroke as the plunger closes under the force of the spring. Thus, if the plunger member is partially or wholly unrestrained by frictional engagement due to opposing force couples or lateral pressure acting on the head, then it will respond continuously and promptly in the intended operating mode in balance between the hydraulic pressure and the opposing spring force.
Also, the dispensing pump of the aforementioned application carries a contoured surface interfacing the stationary piston as an integral part of the plunger head. Thus, when the upper end of the piston and the opposing matching inner end of the plunger head are brought in face-to-face contact during a depression of the head, before the dispensing operation, any air accumulated in the pump chamber is substantially purged by venting it through the discharge as that air is compressed to effect a shifting of the plunger relative to the head for opening the discharge. This contoured surface displaces air volume in the pump chamber and extends into the open upper end of the plunger so that such surface bottoms against the upper end of the stationary piston and ball check members at the end of the plunger head downstroke. Thus, it is possible to exercise the discharge stroke at a velocity producing a pumping rate in excess of the orifice discharge capacity at the controlled design pressure. In accordance with this dispensing pump arrangement, the plunger head reaches the bottom of its stroke while the plunger is still in the valve open mode, displaced from the seat in the head, and continuing the discharge at rated pressure, expelling the accumulated product as the spring force returns the plunger to its seated, valve closed position against the interior of the head. This may be called "after-spray" which could result in unwanted dribbles and drips from the discharge, similar to the inertial "after-spray" of throttling and non-pressure build-up pumps, but which is minimized by the aforedescribed pump arrangements and by the present pump development.